1. Technical Field
The present disclosure relates to electrode thermosurgery systems and, more particularly, to cool-tip ablation electrode systems used for thermosurgery procedures and the like.
2. Background of Related Art
Therapeutic lesions in living bodies have been accomplished for many decades using radio-frequency (RF) and other forms of energy. The procedures have been particularly useful in the field of neurosurgery, typically where RF ablation needle electrodes (usually of elongated cylindrical geometry) are inserted into a living body. A typical form of such needle electrodes incorporates an insulated sheath from which an exposed (uninsulated) tip extends.
Generally, the ablation electrode is coupled between a grounded RF power source outside the body and a reference ground or indifferent electrode for contacting a large surface of the body. When an RF voltage is provided between the reference electrode and the inserted ablation electrode, RF current flows from the needle electrode through the body. Typically, the current density is very high near the tip of the needle electrode, which heats and destroys the adjacent tissue.
In the past, RF ablation electrode systems have incorporated temperature sensors, for example, in the form of a thermistor or thermocouple. In that regard, reference may be made to U.S. Pat. No. 4,411,266 to Cosman, the entire contents of which are incorporated herein by reference, for a detailed discussion of the same. Typically, the sensor is connected to a monitoring apparatus for indicating temperature to assist in accomplishing a desired lesion. As generally known, for a given tip geometry and tip temperature, lesions of a prescribed size can be made quite consistently.
A limitation of prior electrode ablation systems relates to the temperature of the tip. Specifically, prior needle electrodes of a given tip geometry never should effectively exceed a temperature of 100° C. At that temperature, the surrounding tissue will boil and char. Also, uncontrolled disruption, such as hemorrhage and explosive gas formation, may cause extremely hazardous and clinically dangerous effects on the patient. Consequently, the lesion size for a given electrode geometry generally has been considered to be somewhat limited by the fact that the tissue near the tip must not exceed 100° C.
Essentially, during RF ablation, the needle electrode temperature is highest near the tip, because the current density is the highest at that location. Accordingly, temperature falls off as a function of distance from the tip of the needle electrode, and except for possible abnormalities in tissue conductivity and so on, in a somewhat predictable and even calculable pattern. As an attendant consequence, the size of RF lesions for a given electrode geometry have been somewhat limited.
One proposed solution to the limitation of lesion's size has been to employ “off-axis” electrodes, for example the so called Zervas Hypophysectomy Electrode or the Gildenberg Side-Outlet electrode, as manufactured by Radionics, Inc., Burlington, Mass. However, such systems, in requiring multiple tissue punctures, increase the risk of hemorrhage, severely prolong the time of surgery and increase the level of delicacy. Also, an umbrella of off-axis lesions may not produce a desired homogenous or uniform lesion.